X-ray stress measuring apparatus

ABSTRACT

The present invention provides an X-ray stress measuring apparatus wherein two X-ray detectors are simultaneously movable on a circular arc about the incident point of X-rays from an Xray tube in a plane including said incident point and two targets.

D United States Patent [151 3,639,758

Shimura Feb. 1, 1972 [541 X-RAY STRESS MEASURING [56] References CitedAPPARATUS UNITED STATES PATENTS 1 lnvenw" Yflshihim Shim", Tokyo. Japan2,760,055 8/1956 Lasler, Jr ..3 3/56 x 73 Assignee: Rigaku DenkiC(Inpany Limited, Tokyo, 2,948,822 8/1960 Paroselli ..3l3/56 Japan3,030,507 4/1962 Khol ..250/51.5 [22] Filed: Feb 3 1970 3,402,291 9/1968Welnman ..250/51.5

1 1 p 81300 Primary Examiner-William F. Lindquist Atmrney--Alfred W.Breiner [30] Foreign Application Priority Data 3 Mar. 7, 1969 Japan..44/l6875 [57] ABSTRACT The present invention provides an X-ray stressmeasuring ap- [52] US. Cl ..250/51.5, 313/56 a -m wh r in two X-raydetectors are simultaneously [51] Int. Cl. "G011! 23/20 movable on acircular aroabout the incident point f x [58] Field of Search ..250/49.5PE, 51.5, 313/56 from an x ray tube in a plane including Said incidentpoint and two targets.

6 Claims, 4 Drawing Figures X-RAY STRESS MEASURING APPARATUS The presentinvention relates to an X-ray stress measuring apparatus.

Deformation occurs, for example, in welds of metal. To measure theinternal stress of this deformation nondestructively, X-ray diffractioncan be used. Namely, the variation of spacings between crystal latticeplanes due to internal stress is measured. The internal stress may befound from the difference between diffraction angles of X-raysdiffracted on both sides of the incident X-rays by applying'X-rays to aspecimen at a proper angle, generally at 45. Alternatively, X- rays areapplied to a specimen at 90 and at another proper angle, generally 45",and the difference between diffraction angles of both incident X-raybeams is measured. The apparatus according to the present inventionbelongs to the latter method. ln prior arts of apparatuses, in general,an X-ray tube having a single target was used and the diffraction anglesof X- rays incident at 90 and at 45 are measured one after another, sothat the measuring efficiency was low. Further, the target was arrangedon the axis of the X-ray tube and X-rays emitted from the target wereprojected onto the specimen surface. The detector for diffracted X-rayswas arranged sideways of the tube. When the tube is to be brought closeto the specimen to increase the intensity of the incident X-rays,deterioration of the measuring accuracy results, for the angle betweenthe incident and diffracted X-rays cannot be reduced.

The object of the present invention is to provide an X-ray stressmeasuring apparatus having a high-measuring accuracy, wherein an X-raytube is arranged close to the surface of a specimen to increase theintensity of the incident X-rays.

In the accompanying drawing:

FIG. 1 is a cross-sectional front view of an embodiment of the apparatusaccording to the present invention;

FIG. 2 is a side elevation of the apparatus in FIG. 1;

FIG. 3 is a perspective view of a hot cathode of the X-ray tube used inthe apparatus in FIG. 1; and

FIG. 4 is an example of curves measured by the apparatus in FIG. 1.

FIGS. 1-3 show an embodiment of the present invention. The head of anX-ray tube 1 is formed as sector tube, in the center of which a hotcathode 2 is arranged. The cathode 2 comprises a rectangular box-shapedcontrol grid 3 and two hot filaments 4 crossed in said control grid, asshown in FIG. 3. Crossed slits 5, 5' are provided on both sides of thegrid 3. Either of both filaments can be selectively heated. Thefilaments and the grid are connected to a high-voltage cable 7 outsidethe tube through a glass tube 6 extending axially of the tubular head.Arranged on the inside surfaces of gastight tube walls forming bothsides of the sector-shaped tubular head are targets 8 and 9 of desiredmetal in such a way that they are opposed to the slits 5, 5. Andprovided in the inner arcuate gastight wall of the sector-shaped headare windows for X-rays l0 and 11 opposed to the targets 8 and 9,respectively. The outer arcuate gastight wall of the head of the X-raytube 1 carries a baseplate 12 for mounting X-ray detectors, on the outerperiphery of which a circular arc-shaped guideway 13 is formed. TwoX-ray detectors l4 and 15 are slidably mounted on the guideway 13.Further, fixed on the baseplate 12 is a small electric motor 16, towhich a toothed wheel 17 is connected. The hub of the toothed wheel 17is screwed on a threaded rod 18. Links 20 and 21 pivotally mounted onthe end of the threaded rod 18 by means of a pin at 19 are connected atthe other ends to the X-ray detectors l4 and 15 by means of pins 22 and23.

The detector is further equipped with a slit mounting arm 24; 25extending forwardly, and soller slits 26; 27 and 28; 29 are arranged infront of the window 10; ll of the tube and in front of the X-raydetector l4; 15. When one of the crossed filaments is energized andheated and electron beams are projected onto the targets 8 and 9 throughthe slit 5 extending right angles to a tubular shaft of the grid 3, asshown by dotted lines e in FIG. I, X-rays generated from the targetsform parallel X-rays through the soller slits 26 and 27. The X-ray tube1 is so constructed that these X-ray beams xl and x2 intersect with eachother at an angle of 45. The targets 8 and 9 are at equal distances fromthe intersection s and the guideway 13 is a circular arc about the points. The soller slits 28 and 29 are so mounted that the parallel X-raysfrom the point s fall upon the detectors l4 and 15. The links 20 and'2lare equal in length and the threaded rod 18 is arranged in the directionof the bisector of the angle formed by the links 20 and 21. Hence, whenthe motor 16 rotates, the threaded rod 18 moves in the direction ofarrow at and the X ray detectors [4 andv 15 move in the direction ofarrows b and c symmetrically with regard to the X-ray tube.

Such an apparatus is arranged above a specimen of iron, steel or anyother material in such a way that the intersection s of the X-ray beamsxl and x2 projected from the soller slits 26 and 27 lies on the surfaceof the specimen and that the X-ray beam x1 falls upon the specimensurface perpendicularly. Therefore, the X-ray beam x2 falls upon thespecimen surface at an angle of 45". In this condition, the motor 16 isstarted to move the X-ray detectors l4 and 15 symmetrically, forexample, toward the X-ray tube 1. At the same time, the outputs of thedetectors l4 and 15 are applied to an automatic register for recordingthe output I as a function of the displacement angle a of the detector.The register draws two curves as shown by a full and a broken line inFIG. 4. From the difference B between angles at which the two curvestake their maximum, the internal stress of the specimen 30 in thedirection of the intersection of the specimen surface with a planeincluding the X-ray beams x1 and x2 can be estimated.

More particularly, diffracted X-ray beams x3 and x4 are generated fromthe X-ray beams x1 and x2 incident upon the specimen surface 30 at and45. The X-ray detectors l4 and 15 detect the diffracted X-ray beams x3and x4, respectively, so that the angles corresponding to the maximumsof the full and broken lines indicatethe diffraction angles. It is wellknown that the internal stress of a specimen can be calculated from thedifference B of these difiraction angles. In this case, the Braggsformula applies:

2d sin 0=n)t, wherein 0 diffraction angle of X-rays, A= wavelength of X-rays, d spacing between crystal lattice planes of a specimen and n apositive integral number. Assuming that the diffraction angle 0 variesby A0 with variation of the spacing between lattice planes by M causedby the internal stress, the following equation is obtained:

A6=(Ad/ntan 0.

In order to increase the variation A0 to enhance the detecting accuracy,it is, therefore, necessary to make the diffraction angle as near 90 aspossible. Namely, the accuracy can beimproved by lessening the anglebetween X-ray beams x1 and x3 or x2 and x4. Since, in the apparatusaccording to the invention, the hot cathode 2 is arranged in the centerof the tube and the targets 8 and 9 are provided on the inside of thesidewalls, the above-mentioned angle can be made quite small, thuspermitting highly accurate measuring. 0n the contrary, with a constantdiffraction angle 6, the X-ray tube 1 may be brought close to thespecimen surface, so that intensive X- rays are projected to facilitatethe detection of diffracted X- rays. In this case, the measuringaccuracy can be improved by spacing the X-ray detectors enough from thepoint 5.

Further, the apparatus according to the present invention can applysimultaneously two X-ray beams to a specimen at 90 and 45 from an X-raytube and move simultaneously two X-ray detectors, thereby to detectsimultaneously the diffracted X-rays of the respective incident X-raybeams. Hence, the measuring operation can be performed efficiently andrapidly. In addition, errors due to deviation of set positions, as isthe case with the successive measuring method, can be prevented. TheX-ray beam x2 incident obliquely upon the specimen generates diffractedrays on both sides thereof, i.e., thereover and thereunder beam. Theapparatus according to the present invention detects only an X-ray beamx4 diffracted under the incident X-ray beam. Crystal lattice planesparticipating in this diffraction are right angled to the bisector ofthe angles between x2 andur t and form a larger angle against thespecimensurface than those which participate in the upside diffraction,so that the spacing between them greatly varies with a stress parallelto the specimen surface. Therefore, the measurement is possible with ahigher accuracy than the upside diffracted rays are detected.

The above description applies in case of measurement with parallelX-rays. Measurement by concentration method is possible by heating the;hot filament arranged in the axial direction of the X-ray tube 1 toproject electron beams through the slit 5' of the grid 3 to the targets8 and 9 and to form a focal line of X-rays perpendicular to the drawingplane of FIG. 1. In this case, the soller slits 26-29 are removed andfiner slits are so mounted on the arms 24 and .25 that they are on acircular are, shown by a dot-and-dash line p, passing through theposition of said focal line about the point s. it is also possible tomeasure simultaneously the internal stresses in two perpendicularlyintersecting directions, if a cathode is arranged in the center of atube and three targets are provided on the inside surface of the tubewall.

What is claimed is:

1. An X-ray stress measuring apparatus comprising a hot cathode arrangedin the center of an X-ray tube, at least two X-ray generating targetsopposed to said cathode and arranged on the inside surfaces of saidtube, said targets applying X-rays to the surface of a specimen on thesame position at and at any other desired angle; two X-ray detectorsarranged outside said targets, means for moving each of said X raydetectors symmetrically in relation to the X-ray tube, a register forrecording the relationship between the displacement angle of eachdetector and the output thereof, whereby the internal stress of aspecimen in the direction of the intersection of the specimen surfacewith a plane including the two X-ray beams can be estimated from thedifference between the displacement angles at which peak outputs areobtained from the two detectors.

2. The apparatus of claim 1 wherein said X-ray tube has a sector-shapedtubular head and said targets are arranged on the inside surfaces of thesector walls of said tubular head.

3. The apparatus of claim 2 wherein said tubular head includesabaseplate for mounting said detectors.

4. The apparatus of claim 3 wherein the outer periphery of the baseplateforms a circular arc-shaped guideway and said detectors are slidablymounted thereon.

S. The apparatus of claim 1 wherein said cathode comprises a rectangularbox-shaped control grid and two hot filaments in said grid.

6. The apparatus'of claim 5 wherein said filaments are selectivelyheated.

1. An X-ray stress measuring apparatus comprising a hot cathode arrangedin the center of an X-ray tube, at least two X-ray generating targetsopposed to said cathode and arranged on the inside surfaces of saidtube, said targets applying X-rays to the surface of a specimen on thesame position at 90* and at any other desired angle; two X-ray detectorsarranged outside said targets, means for moving each of said X-raydetectors symmetrically in relation to the X-ray tube, a register forrecording the relationship between the displacement angle of eachdetector and the output thereof, whereby the internal stress of aspecimen in the direction of the intersection of the specimen surfacewith a plane including the two X-ray beams can be estimated from thedifference between the displacement angles at which peak outputs areobtained from the two detectorS.
 2. The apparatus of claim 1 whereinsaid X-ray tube has a sector-shaped tubular head and said targets arearranged on the inside surfaces of the sector walls of said tubularhead.
 3. The apparatus of claim 2 wherein said tubular head includes abaseplate for mounting said detectors.
 4. The apparatus of claim 3wherein the outer periphery of the baseplate forms a circular arc-shapedguideway and said detectors are slidably mounted thereon.
 5. Theapparatus of claim 1 wherein said cathode comprises a rectangularbox-shaped control grid and two hot filaments in said grid.
 6. Theapparatus of claim 5 wherein said filaments are selectively heated.